Habitat change

The human modification of the Earth’s land
surface has been taking place for thousands of years for food and
to obtain other resources. However, the current rate, extent and
intensity of change is far greater than has been experienced ever
before. That is driving unprecedented changes in ecosystems and
environmental processes.

The conversion of primary forest to
semi-natural, agricultural habitat is among the most extreme change
(for example, loss of tropical and semi-tropical rainforest to palm
oil plantations). Such deforestation has the potential to cause
problems on a global scale and a clear link has been demonstrated
between forest loss and climate change.

In addition, habitat losses can result
from:

Changes in farming practices, such as intensity of cultivation
and changes in crop types

Expansion of transport networks

Urban development

Mining and quarrying

Recreational use

Biodiversity is often reduced dramatically by
changes in land use. The area and condition of suitable habitat can
be reduced, patches of habitat can be lost and remaining habitat
can become fragmented. After a change in use conditions may no
longer be suitable for a species to survive and individuals may be
unable to move elsewhere.

Rivers

In many countries, including most developed
countries, it is rare to find a river that has not been profoundly
altered by human use. Natural rivers are dynamic and
changeable with many freshwater and wetland habitats and species
along their course that rely on the habitat.

People have made intense use of rivers. They
have been altered to provide energy, from water mills to modern
hydroelectric power. They are often straightened or canalised
to free up land for farming and to carry flood waters away as
quickly as possible. Many are blocked or impounded to form storage
reservoirs.

Water is used for farming, industrial use and
for drinking and is taken from rivers directly or from underground
sources, both of which reduce river flows. Food has always been
harvested from rivers and they are also used for transport and
recreation.

Some of these uses are in conflict with each
other and not all are sustainable. For example, rivers are
straightened, widened and canalised to protect nearby land, but
over time changes can alter the performance of the river upstream
and downstream leading to flooding elsewhere. Together with land
use changes in the catchment, such as ploughing up grassland and
improving agricultural drainage, it can exacerbate both droughts
and floods.

Reservoirs for water storage also have an
impact. They can interfere with water quality and flows downstream,
with the migrations of fish and may be vulnerable to silting.

Human engineering of rivers has reduced
biodiversity. However, sustainable approaches to management can
prevent flooding by restoring natural, diverse river corridors and
can deliver biodiversity increases too.